Arya used that secret passage twice lol. Once when she discovers it after hearing Varys and Illyrio scheming, and again to get outside the Keep when the Lannisters started slaughtering the Stark bannerman.

Dude HALF OF THE CHARACTERS LIVED IN KINGS LANDING FOR SEVERAL YEARS. Why the fuck is Arya just aimlessly running around!? SHE'S MRS. FUCKING I HAVE A PLAN. WHO EVEN WAS THAT CHARACTER ugh I'm still so upset I'm sorry

I dunno maybe because there was a fucking Dragon torching every house in the city. Massive crowds of people in chaos. Armies fighting in the streets... Season 8 has been a shit show but damn this is such a nitpicky complaint.

I know I know but man, there are 500,000 people who are terrified and burning alive running around in a relatively compact area. Plus two fighting armies and a Dragon burning EVERYTHING! Even if you’re a trained assassin (one who is like 5’2 110 lbs) in all that isn’t going to be able to just waltz out. Now, I would’ve preferred that scene follow Davos or Jon or someone else rather than Arya but... I think it is a little nitpicky when there are massive writing failures all over this season to complain about. Though, I read further down below and people are complaining the dragon fire so whatever complain all you want.

I wonder if there is like an administrative assistant somewhere in the Red Keep to book the room for all your plotting needs, you wouldn't want to double book your plotting sessions in the skull room.

- Varys clearly knows about it, and likely had Illyrio come up from the ocean via the waterway, to meet him there

- Tyrion knows about it, because of course he does, and because he tells Jaime to use it to escape

- Jaime almost assuredly already knew about it, because he'd be a fucking terrible former captain of the Kingsguard if there was a cave under the Red Keep that led, unguarded, into the room where you keep all the dragon skulls, let alone into the Red Keep itself

- Arya knew about it from her chasing cats days

- I feel like we saw Littlefinger down there at some point plotting with someone (Varys was it?)

- Joffrey mentions the dragon skull room

- Euron knows about it, probably, because why else would he swim his ass to a random part of the rocky cliff unless his intention was to go up the stairs into the Red Keep too

Honestly it couldn’t have been that great of a secret, it housed a very infamous dragon skull and was a pretty massive. Robert had the Skull taken out of the throne room and put down there so a lot of people would have to know about it.